[U-Boot] [RFC] Make U-Boot log great again

[Wolfgang Denk]

Dear Lukasz,

In message <20180220105933.7d402043 at jawa> you wrote:
>
> > That patch intent was to keep the current behaviour as is for all
> > users, so the fact that you now have the FAT environment enabled is an
> > unwanted side-effect.
> 
> The same situation is on Beagle Bone Black. Even though with OE it is
> built to use eMMC for storing its envs, by default it also has envs in
> FAT support enabled.
> 
> For that reason, u-boot on this board looks for envs in FAT first and
> similar message is printed.
> 
> IMHO, we now have (unintentionally) the situation where implicitly
> reading envs from FAT has the highest priority.

This makes clear that this area needs more than just a casual "fix".
We must make sure to implement a policy that is consistent and
useful:

1. The user should be able to select which devices are probed for
   the environment.
2. He should be able to specify the exact order in which this
   probing takes place.
3. Enough information should be printed so the user knows where his
   environment is coming from, and which devices may have been
   probed without success.  The messages should be clear and easy
   to understand.

Obviously it is not possible to adjust this configuration at
run-time - accessing some environment variable to determine where to
read the environment from is a nice chicken-and-egg problem.  So
this is some _compile time_ configuration, i. e. it probably
requires some Kconfig magic plus appropriate code changes.

Just fixing an error message is not enough.

Best regards,

Wolfgang Denk

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